Connecting Through a Wireless Network

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Chapter 6

• Connecting Through a Wireless Network

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Current Wireless Networking Technologies

• Two drawbacks of wire-based networking
• Tangle of wires connecting computer and
  peripherals
• Cost of pulling wires through walls, ceilings,
  floors
• Wireless media are forms of electromagnetic
  radiation
• Three major current wireless networking
  technologies
• Radio wave technologies (short range)
• Infrared technologies (short range)
• Terrestrial and satellite microwave technologies
  (long range)

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A Short History of Wireless Networks

• Packet radio early PC networking over radio
  waves
• Developed by amateur (ham) radio operators
• Wireless standards develop in parallel with ham
  radio
• 1985 Industrial, Scientific, Medical (ISM) band
  opened
• Telecommunications Act of 1996
• IEEE 802.11 standard set in 1997
• A few of the entities influencing standards
• IEEE (Institute of Electrical and Electronics
  Engineers)
• IETF (International Engineering Task Force)
• ISO (International Organization for
  Standardization)

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Radio Wave Technologies

• Frequency ranges of various transmission types
• AM 5351605 kilohertz (kHz)
• FM 88108 megahertz (MHz)
• Network 902-928 MHz, 2.4-2.4835 GHz, 5-5.825 GHz
• Directional signal transmitted between buildings
• Transmission involves sending and receiving
  antennas
• Wave is short in length and low-power (1-10
  watts)
• Suitable for line-of-sight transmission
• Signal goes from point to point on earth's
  surface
• Limitations due to interruptions, such as hills
• Data capacity range 1 Mbps to 54 Mbps

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Radio Wave Technologies (continued)

• Spread spectrum technology for packet
  transmissions
• Spreads transmission over adjoining frequencies
• Frequency range 902928 MHz range
• Data transfer range 154 Mbps
• Advantages to radio wave communications
• Useful in situations where portable computers
  deployed
• Relatively easy and inexpensive to install
• Disadvantages to radio wave communications
• Some networks cannot match high-speed (100 Mbps)
• Interference from other operators and natural
  obstacles
• Inadequate security

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IEEE 802.11 Radio Wave Networking

• IEEE 802.11 group most influential wireless
  standards
• Includes 802.11, 802.11a, 802.11b, 802.11g
• Communication with 802.11 devices is
  non-proprietary
• Features of 802.11 standards
• Encompass either fixed or mobile wireless
  stations
• Involve two kinds of communications
• Asynchronous discrete units with start and stop
  bit
• Synchronous signal has timing restrictions
• Support SNMP protocol and network authentication
• Operate at two lower OSI layers Data Link and
  Physical

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Wireless Components

• Three components transceiver, access point,
  antenna
• Wireless NIC (WNIC) transceiver card
• Functions as transmitter and receiver
• Operates at Physical and Data Link layers of OSI
  model
• May be internal (PCI card) or external (USB key
  fob)
• Access point interfaces WNIC and cable network
• Examples bridge, switch, or router
• Antenna device radiates and receives radio waves

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Directional Antenna

• Sends radio waves in one main direction
• Amplifies signal better than omnidirectional
  antenna
• Gain amplification of radiated signal
• Application transmitting signals between
  buildings
• Each building has an antenna
• Antennas connected to access points
• Signal has more gain in one direction
• Small portion of signal is radiated outward

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Omnidirectional Antenna

• Radiates radio waves in all directions
• Diffused signal likely has less gain than
  directional type
• Application indoor network
• Mobile users need to send and receive in all
  directions
• Signals moving over shorter distances require
  less gain
• Omnidirectional antenna deployed varies with
  device
• WNIC on portable devices use snap-on antenna
• Access point for indoor network
• May have a snap-on antenna
• May connect to antenna using cable
• Outdoor access point connects to antenna via cable

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Wireless Networking Access Methods

• Two access methods priority-based and CSMA/CA
• Priority-based access (or point coordination
  function)
• Intended for time-sensitive communications
• Access point functions as point coordinator
• Point coordinator establishes contention-free
  period
• Method revolves around contention-free period
• Carrier Sense Multiple Access with Collision
  Avoidance (CSMA/CA)
• Also called the distributed coordination function
• CSMA/CA works to avoid collisions

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802.11b

• Outlines speeds in the 2.4 GHz frequency range
• Minimum speed 1 Mbps
• Maximum speed 11 Mbps
• Uses Direct Sequence Spread Spectrum (DSSS)
• How DSSS radiates data signal over radio waves
• DSSS spreads data across any of up to 14 channels
• Each channel up to 22 MHz in width
• Number and frequency of channels based on country
• Data signal sequenced over channels
• Data signal amplified for gain
• Barker Code/CCK enhance DSSS over 5.5 Mbps

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802.11g

• Allows three transmission methods on 2.4 GHz band
• OFDM (native mode)
• Similar to OFDM under 802.11a (different bands)
• Minimum speed 6 Mbps
• Maximum speed 54 Mbps
• Complementary Code Keying (CCK)
• Used with DSSS for backward compatibility with
  802.11b
• Minimum speed 1 Mbps
• Maximum speed 11 Mbps
• Packet Binary Convolution Code (PBCC)
• Unofficial extension for 802.11b
• Offers speeds of 22 Mbps and 33 Mbps

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802.11g (continued)

• Restrictions and considerations using 802.11g
• Devices must support minimum speeds by standard
• Speed values 1, 2, 5.5, 6, 11, 12, and 24 Mbps
• Slightly shorter range than 802.11b
• More access points may be needed
• Smaller bandwidth (90 MHz) than 802.11a or
  802.11b
• No more than three access points in given area
• Devices combine with 802.11b devices on one LAN
• Advantage retain earlier investment in 802.11b
• Disadvantage lowers network performance

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Open System Authentication

• Allows any two stations to authenticate each
  other
• Used by default by many vendor devices
• Simple method
• Sender requests authentication from destination
• Authentication complete when receiver verifies
  request
• Security value of open system authentication is
  low

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Shared Key Authentication and Wired Privacy (WEP)

• Employs Wired Equivalent Privacy (WEP)
• WEP encryption key
• Consists of key, checksum, initialization
  information
• Total key length is 64- or 128-bits
• 128-bit key supports superior 128-bit encryption
• Up to four WEP keys can be stored in key index
• Authenticating using shared key and WEP
• Sender requests authentication from another
  station
• Contacted station sends back challenge text
• Sender encrypts challenge text, returns to
  challenger
• If returned text properly decoded, verification
  sent

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Wi-Fi Protected Access (WPA)

• An improvement on and is expected to replace the
  original Wi-Fi security standard, WEP.
• Uses Temporal Key Integrity Protocol (TKIP)
• WPA provides "strong" user authentication based
  on 802.1x and the Extensible Authentication
  Protocol (EAP).
• WPA depends on a central authentication server
  such as RADIUS
• Remote Authentication Dial In User Service
• Using authentication, authorization and
  accounting (AAA) Protocol

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Extra RADIUS

• A protocol for remote user authentication and
  accounting.
• Enables centralized management of authentication
  data, such as usernames and passwords.
• When a user attempts to login to a RADIUS client,
  such as a router, the router send the
  authentication request to the RADIUS server.
• The communication between the RADIUS client and
  the RADIUS server are authenticated and encrypted
  through the use of a shared secret, which is not
  transmitted over the network.
• The RADIUS server may store the authentication
  data locally, but it can also store
  authentication data in an external SQL database
  or an external Unix /etc/passwd file.
• RADIUS is the de facto authentication provider in
  802.11i wireless networks.

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Service Set Identifier

• SSID identification value up to 32-bits in
  length
• Value defines logical network for all member
  devices
• Examples of SSIDs
• Series of random characters
• String identifying network purpose, such as
  "Atmospheric Research"
• SSID often configured by default
• Ensure that vendor default is replaced
• Use SSID value difficult to guess

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Extra SSID

• The SSID differentiates one WLAN from another,
  so all access points and all devices attempting
  to connect to a specific WLAN must use the same
  SSID.
• Because an SSID can be sniffed in plain text
  from a packet it does not supply any security to
  the network.
• An SSID is also referred to as a network name
  because essentially it is a name that identifies
  a wireless network.

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802.1x and 802.11i Security

• 802.1x wireless and wired authentication
  approach
• Port-based form of authentication
• Ports over which connection made act in two roles
• Uncontrolled allows unauthenticated
  communications
• Controlled allows only authenticated
  communications
• Node roles supplicant and authenticator
• Disadvantage authentication process not
  encrypted
• 802.11i adds three features to enhance 802.1x
• Temporal Key Integrity Protocol (TKIP)
• Advanced Encryption Standard (AES)
• Robust Secure Network (RSN)

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Extra 802.1x

• 802.1X An authentication standard for wired and
  wireless LANs, used to identify users before
  allowing their traffic onto the network. It can
  be used in wireless environments to authenticate
  users for more secure WEP, Wi-Fi Protected Access
  or 802.11i deployments.
• The user or client that wants to be authenticated
  is a supplicant.
• The actual server doing the authentication,
  typically a RADIUS server, is called the
  authentication server.
• And the device in between these two elements,
  such as a wireless access point, is called the
  authenticator.

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802.11 Topologies

• Independent basic service set (IBSS) topology
• Consist of two or more stations in direct
  communication
• Peer-to-peer communication between WNICs on nodes
• Stations often added on impromptu basis
• Extended service set (ESS) topology
• Deploys one or more access points
• Enables more extensive area of service than the
  IBSS
• Network sizes range from small to large

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Alternative Radio Wave Technologies

• Three popular alternatives to 802.11 group
• Bluetooth
• HiperLAN
• HomeRF SWAP
• Alternative standards supported by specific
  vendors

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Bluetooth

• Defined through the Bluetooth Special Interest
  Group
• Characteristics
• Uses Frequency Hopping Spread Spectrum (FHSS)
• Frequency hopping packets hop among 79
  frequencies
• Occurs in 2.4 GHz range (2.42.4835 GHz)
• High wattage transmission from 10 to 100 meters
• Can use asynchronous or synchronous communication
• Uses time division duplexing (TDD)
• Packets sent in alternating directions using time
  slots
• Many kinds of wireless products use Bluetooth
• Examples PDAs, keyboards, mice, printers, others

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Infrared Technologies

• Broadcasts in single direction or all directions
• Advantages of infrared medium
• Inexpensive
• Difficult to intercept
• Not prone to RFI or EMI
• Disadvantages of infrared medium
• Slow data transmissions
• Does not penetrate walls
• Experiences interference from strong visible
  light
• Diffused infrared reflects infrared light from
  ceiling
• Defined by IEEE 802.11R standard
• Communication with pulse position modulation (PPM)

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Wireless MANs

• Based on IEEE 802.16 standard (WiMAX)
• Provides connectivity up to 75 Mbps
• Has a reach of up to 30 miles
• WiMAX called connection for "last mile"
• Connects home or office to wired network provider
• Implementing WiMAX for rural office
• Install wireless communication at network
  provider
• Include a directional or omnidirectional antenna
• Connect directional antenna to wireless router in
  office
• Point office antenna to provider's antenna

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Microwave Technologies

• Work in one of two ways terrestrial and
  satellite
• Have theoretical bandwidth up to 720 Mbps

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Terrestrial Microwave

• Characteristics of transmission
• Between two directional parabolic antennas
  (dishes)
• Performed in ranges of 46 GHz and 2123 GHz
• Require the operator to obtain an FCC license
• Uses of terrestrial microwave transmission
• Where cabling costs are too high
• Where cabling and wireless options not possible
• Example between two large buildings in a city

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Satellite Microwave

• Transmits signal between three antennas
• One antenna on a satellite in space
• Connection speed at 1.5 Mbps
• May be "throttled" down for uploading large files
• Also vary due to weather, signal strength, usage
• User equipment needed for satellite communication
• Satellite dish about 2 or 3 feet in diameter
• Digital modems to transmit and receive signals
• Coaxial (TV-like) cables from the modems to dish
• Serial/USB cable from modems to serial/USB ports
• Software from provider to enable computer setup

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Satellite Microwave (continued)

• Geosynchronous satellites
• Orbit at 22,300 miles above the Earth
• Orbital position stationary with respect to earth
• Extreme distance can cause transmission delays
• Low Earth orbiting (LEO) satellites
• Orbit between 435 and 1000 miles above the Earth
• Facilitate faster transmission of two-way signals
• Uses of satellite networks
• Broadband (high-speed) Internet communications
• Around-the-world video conferencing
• Classroom and educational communications
• Other communications involving voice, video, data

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Wireless Hotspots

• Locations that provide a public access point to
  users
• Examples student union, library, airport, hotel
• Considerations when setting up hotspot
• Implementing WEP or WPA
• Directing public users to instructional Web pages
• Learning about acceptable uses of hotspots
• Learning how to configure security

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Designing a Wireless Network

• Guidelines
• For home/office installations consider using
  802.11g
• Choose router as access point
• Router manages traffic and acts as firewall
• Increase speed of network
• Use more access points to speed up network
• Shorten distances between nodes for faster
  network
• Avoid combining 802.11b and 802.11g (reduces
  speed)
• Use WiMAX for applications spanning several miles
• Use WEP or WPA and 802.1x/802.11i for security
• Always configure the SSID for a little extra
  security